Shredded tungstens welding Aluminum with mixed AC/DC

Gavin Melville · Sat Oct 17, 2015 2:42 am

I've been using mixed arc for welding Aluminum for a while, and weld wise all is good. I run 200 ish amps DC, 60% of the time, AC at 60% of that current. The AC is 250Hz, square wave, 62.5% EN. I am welding thin to thick, say 1" to 1/8", and get deep penetration and narrow welds.

The problem is tungsten life. The ends of the tungstens are shredded, like when you get a split, except I get 20 splits. Tried all kinds, zirconium doped, lanthanated, even thorium doped. The best results are with rare earth (E3) in 1/8", one size up from what I usually use. They still shred, but last longer. Prep is a short cone, no ball as per Kemppi's recommendation. I end up regrinding every 10 minutes.

Is anyone else running mixed AC/DC on Aluminum?

TRACKRANGER · Sat Oct 31, 2015 8:45 pm

I'm not running mixed DC/AC but am interested in your other settings

Your AC is 250Hz, Square, 62.5% EN - OK

What is the switching frequency of the DC to AC?

Are you running EN in the DC part of the cycle?

200 Amps on a 1/8" electrode should be OK.

What gas? Is it a Argon/Helium mix?

Gavin Melville · Tue Nov 03, 2015 5:19 pm

The DC / AC switching rate is 0.6Hz, and the DC is EN. Gas is pure Argon.

I may have found the problem, or at least part if it. I have lengthened the post gas time to 15 seconds. I suspect the electrode runs very hot in AC/DC mode, and needs gas flowing for longer to let it cool. The electrodes still look somewhat shredded, but not as bad, and now they are shiny. A work in progress.

TwentyFourSeven · Wed Nov 04, 2015 10:49 pm

Only tungsten i have found that hasnt shreded tips has been the white band. I believe its zirconiated but you said you have tried that. Lanthonated and thoriated both split ends real bad on me. The white does a nice clean balled tip.

ex framie · Thu Nov 05, 2015 4:56 pm

Noob question if I can interrupt, what is mixed dc/ac?

Gavin Melville · Sun Nov 08, 2015 3:20 am

Running DC on aluminium part of the time, AC the rest, about 1/2 a second of each. The DC gives a tight arc with good heating, the AC does the cleaning. In my case welding 6061 aluminium where the thickness of the thick to thin metal is approx 10 to 1. It's noisy, looks good (auto dime maker), but blows the end off tungsten's. In all this is quite useful.

Been discussing it here;

http://www.mig-welding.co.uk/forum/thre ... -dc.58374/

ex framie · Sun Nov 08, 2015 5:07 pm

Thanks Gavin.

TwentyFourSeven · Mon Nov 09, 2015 8:14 am

Does running on DC melt the metal faster?

Gavin Melville · Mon Nov 09, 2015 2:47 pm

The narrow focused arc melts the metal faster, the area is smaller. It's like welding Aluminum with the arc width and shape you get on Stainless. In my case I can use the penetration on the heavier metal, and run the AC on the thinner metal.

TwentyFourSeven · Tue Nov 10, 2015 10:37 pm

DC+ or DC-?

Gavin Melville · Wed Nov 11, 2015 6:56 pm

DC-.

DC+ would do bad things.

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soutthpaw · Mon Nov 16, 2015 10:40 am

DC+ and a block of copper is great for balling tungsten with a transformer machine. Then switch to DC- to weld and you have a perfectly prepared tungsten to weld with

d.smith · Mon Nov 16, 2015 2:54 pm

How are you grinding/cutting your tungsten to size? someone once told me that if you are using pliers or a tool to cut or snap it it may create small stress fractures in your tungsten and will split the ends while welding AC. The fix was to use a cut off wheel to cut to size then grind it. my tungsten splitting has been minimal since then.

hope that may help you.